Moderate renal impairment does not preclude the accuracy of 24‐hour urine normetanephrine measurements for suspected pheochromoctyoma

Objective A 24‐hour urine nor/metanephrine (urine NM‐MN) measurements are a recommended first step in pheochromocytoma diagnosis. We hypothesized the presence of renal impairment (CKD) significantly confounds the results obtained in a urine NM‐MN collection, giving artificially lower measurements. Design Retrospective review of a comprehensive laboratory database with all urine NM‐MN results from Southern Alberta from 2010 to 2018 (n = 15 505). After excluding high probability pheochromocytoma cases, results from patients with three levels of CKD (n = 796) were compared to those without CKD to determine the potential CKD effect. Patients All patients having urine NM‐MN collection during the time period, irrespective of ordering physician or test indication. Measurements Urine NM‐MN was measured by liquid chromatography‐tandem mass spectrometry and glomerular filtration rate determined within a median of 1.9 days, as estimated by CKD‐EPI equation. Results In subjects with mild‐to‐moderate renal impairment, there was no continuous gradient between subnormal renal function and urine NM‐MN measures. When the estimated GFR was < 15 mL/min/m 2 , the hypothesized effect on lowered urine NM‐MN became apparent. Conclusions A 24‐hour urine NM‐MN measurement is unlikely to be affected by mild‐to‐moderate renal impairment and may be used as a reliable diagnostic test. With more advanced renal impairment, CKD‐specific reference ranges or an alternative test may be needed.